The mobile telecommunications industry has been growing at a rapid rate, owing in part to the increased mobility of its customers and in part to the decrease in the cost of the complex electronic circuits that are found in mobile transmitters and receiving apparatus. With the proliferation of mobile telephone equipment, and the anticipated surge of usage that is likely to occur as a result of personal communications networks and services, it is now and will be quite common to encounter mobile telephone users not only in automobiles and other vehicles but also as pedestrians carrying portable units.
Currently, the most popular form of mobile telephone service is provided by the cellular telecommunication industry. Each cellular user typically subscribes to service with a carrier in a particular geographic region served by that carrier. Calls to the subscriber when in the home region are easily completed, since they are routed to and through a Mobile Telephone Switching Office (MTSO) that includes a database which translates information extracted from the incoming call into signaling information necessary to alert the subscriber. When the subscriber is located in a different region, he or she is designated a "roamer", and call completion becomes more difficult. This is because it is not known, a priori, to which MTSO to route the call. Even if the region in which the roamer is located is known in advance, the MTSO serving that region will not normally contain the translation information necessary to complete the call.
To overcome the roamer problem, various systems have been devised in which a cellular subscriber notifies his or her MTSO that he is or will be located in another geographic area. This allows the necessary information to be transmitted from the "home" MTSO to the "host" MTSO, to provide the translation required for completion of the calls to the roamer. One approach involves a system for automatically updating a database containing the roamer's current location, as described in U.S. Pat. No. 4,901,340 issued to R. C. Crouse et al. on Feb. 13, 1990. This solution does not, however, provide for seamless and ubiquitous connections to roamers, because it is first necessary for individual cellular providers to establish cooperative business relationships with each other and then to implement these relationships by the interconnection of compatible signaling systems, either directly or through third-party roamer management systems.
If the location of the roamer is not available in a database accessible to the MTSO, the roamer can nevertheless be contacted by using land-based or satellite paging. One example of a roaming system which uses paging to reach the roamer is described in an article entitled "Satellite Paging in Cellular Communications" by G. Maile, which appeared in the Proceedings of the International Conference on Cellular and Mobile Communications, p.205-13, published by Online Publications, Pinner, UK, in 1985. According to the author, the expectation that calls can be made and received anywhere has placed significant demands on the mobile terminal paging operation, thereby motivating an alternative approach based on satellite transmission of the paging data.
Another article that describes the development of radiopaging in Europe and an overview of European systems that enable a "roaming" service to be provided across national boundaries, is contained in Telecommunications, vol 21, no. 11, p 35-47, November 1987.
In currently available paging systems, when a cellular subscriber is signaled, he or she can receive alphanumeric messages such as the calling party's name and/or phone number. Depending on the nature of the message, the cellular subscriber (called party) can return the call by initiating a new call immediately or at a later time, as appropriate. However, a real time connection (on the same call that caused generation of the paging signal) between the calling party and the cellular subscriber is not made at that time. The called party must, instead, initiate a call back based upon information received from the page. This call may reach the calling party, but the likelihood of call completion is reduced by the fact that the calling party has no indication or expectation that a return call is imminent, and thus may not be available at the same location to actually receive the call. If the return call cannot be completed, the next best option currently available is to connect the cellular subscriber to a voice mail box, in which a message has been left.